This invention relates to measuring devices and more particularly a density measuring device which permits continuous operation as it traverses the surface of the material whose density is being measured.
In certain paving operations, such as, for example, when a layer of asphalt is applied to a pre-existing concrete roadway, the asphalt is commonly applied with a paver which lays the material at a preselected thickness. Typically, a roller is then employed for compacting the material. The actual density of the asphalt will be influenced by a number of factors, including the vibration frequency and amplitude of the compactor, ballast, the forward travel speed, the temperature of the material, the degree of overlap, the number of roller passes and roller travel speed, and the reaction surface to which the material is being applied. The thickness of the material being applied may also affect the efficiency of the compactor and therefor, influence density.
It is important to know the material density to prevent over-rolling. This occurs when the maximum density of the material has been attained and further compaction thereafter tends to loosen the material. Also, in the compaction of asphaltic concrete, it is important to know how close the compactor can approach the asphalt paver and how far behind it can traverse before chilling is encountered. If the compactor is too close to the paver, the hot material displaces and cannot be compacted. On the other hand, if the roller trails the compactor by too great a distance, the material will cool excessively at the far end of the traverse so that compaction in that area is also not possible.
It is, therefore, desirable to provide a method for rapidly and accurately determining the density of an applied layer while it was still hot so that corrections in the compacting operation can be made to eliminate the necessity for costly reworking.